A popular practice in contemporary music is to provide sound amplification systems for musical instruments by using electromechanical transducers. The transducers convert some portion of the instrument's mechanical energy, such as that in a vibrating string, into an electrical signal which is amplified and used to drive a loudspeaker. There are two principal types of musical transducers, or pickups, in common use: magnetic pickups and piezoelectric pickups. Both of these types of pickups have inherent limitations and undesirable characteristics which affect the quality of the amplified sound.
Piezoelectric pickups respond to pressure and must be in mechanical contact with the instrument. Musical tones are communicated to the pickup via the mechanical contact. An undesirable characteristic of piezoelectric pickups is that ambient noise, as well as vibration and shock from handling of the instrument, is also picked up and amplified. Another limitation of such piezoelectric pickups is that the sound produced by the instrument cannot be separated into its constituent tones or voices. The piezoelectric transducer only picks up the complete or composite sound from the instrument and amplifies the one, total signal. In addition, piezoelectric pickups do not respond well to low frequencies and they suffer from an irregular frequency response.
The use of magnetic pickups requires that the instrument's vibratory elements, whether strings, bars, or reeds, be made of magnetically permeable materials. An undesirable characteristic of magnetic pickups is clearly that these vibratory elements must be conductive surfaces which can be a potential electric shock hazard to the musician who must be in contact with them. In addition, the induction coils typically used in magnetic pickups are sensitive to hum and ambient electrical noise and have an undesirable resonance in their frequency response.
Modern technology has made it possible to use a standard polyphonic musical instrument to control a multi-channel musical synthesizer. Another recent development is the possibility of automatic musical score transcription, such as direct transcription from musical performance to printed manuscript. Any electromechanical transducer used for these purposes must provide independent output channels for each string or musical tone source. The channels must have very high isolation and independence to be effective for these purposes. Because these requirements have been very difficult and expensive to accomplish using the traditional technologies of magnetic and piezoelectric transducers, a need has arisen for a new type of transducer.
Many of the inherent limitations of magnetic and piezoelectric pickups have been eliminated by the development of optoelectric pickups for musical instruments. These devices, however, have been limited to string instruments and have suffered from the adverse effects of ambient light from sources such as stage lights and spot lights used during musical performances. Therefore, a need exists for an optoelectrical pickup for musical instruments, other than just string instruments, which is insensitive to ambient light; which is small, lightweight, and adaptable to many different instruments; and which overcomes the problems of magnetic and piezoelectric pickups.